linux-kernel - [PATCH 3/4] KVM: x86: WARN and reject loading KVM if NX is supported but not enabled

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Message-Id: <20210615164535.2146172-4-seanjc@google.com>
Date:   Tue, 15 Jun 2021 09:45:34 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] KVM: x86: WARN and reject loading KVM if NX is supported
 but not enabled

WARN if NX is reported as supported but not enabled in EFER.  All flavors
of the kernel, including non-PAE 32-bit kernels, set EFER.NX=1 if NX is
supported, even if NX usage is disable via kernel command line.  KVM relies
on NX being enabled if it's supported, e.g. KVM will generate illegal NPT
entries if nx_huge_pages is enabled and NX is supported but not enabled.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index acc28473dec7..1f6595df45de 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10981,6 +10981,9 @@ int kvm_arch_hardware_setup(void *opaque)
 	int r;
 
 	rdmsrl_safe(MSR_EFER, &host_efer);
+	if (WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_NX) &&
+			 !(host_efer & EFER_NX)))
+		return -EIO;
 
 	if (boot_cpu_has(X86_FEATURE_XSAVES))
 		rdmsrl(MSR_IA32_XSS, host_xss);
-- 
2.32.0.272.g935e593368-goog